The invention relates to an antitheft protection system for a vehicle having at least one transmitting and receiving unit connected to the vehicle, at least one code transmitter, which can communicate with the at least one transmitting and receiving unit, and at least one base unit, which can communicate with the at least one transmitting and receiving unit.
The invention furthermore relates to a method for operating an antitheft protection system for a vehicle, in which at least one transmitting and receiving unit connected to the vehicle communicates with at least one code transmitter, and at least one base unit communicates with the at least one transmitting and receiving unit.
Furthermore, the invention relates to components of an antitheft protection system.
Generic systems, methods and components often serve as a replacement for the mechanical locking systems that are conventionally present on a motor vehicle. The systems operate on the basis of a code which is communicated by a code transmitter to a receiving unit in a motor vehicle. Generally, a plurality of transmitting and receiving units equipped with antennas are arranged at different positions on the vehicle, thereby ensuring that the signals communicated by the code transmitter are received. The presence of transmitting and receiving units on different sides of a vehicle can additionally provide a side selectivity based on which the side of the vehicle on which the person actuating the code transmitter is situated is identified.
The signals received by the transmitting and receiving units are then forwarded within the vehicle to a base unit or control unit, in which they are evaluated. This base unit generally communicates with the vehicle bus, so that if appropriate, that is to say in particular in the case of a correct code, actuation of the locking system of the vehicle can be initiated.
In addition to the code which is communicated by the code transmitter, it is possible to use further criteria for the actuation of the locking system. For security reasons, it may be desirable, for example, to permit opening only when the code transmitter is not beyond a specific maximum distance, for example 6 m. The risk of inadvertent actuation of the locking system can be reduced in this way. Such a maximum distance can be realized for example by using electromagnetic fields with limited range for the communication, so that distance limitation is intrinsically present. However, it may also be desirable, in principle, to enable larger communication distances and to utilize the knowledge of the present distance between the code transmitter and the vehicle for providing special functionalities. For example, it may be practical to switch on the interior light of the vehicle by actuating a code transmitter even at a distance of, for example, 8 m from the vehicle—therefore, communication must already be possible at this point in time, while actuation of the locking system should not yet be possible—and to enable opening of the vehicle only at a distance of, for example, 2 m. For this purpose, systems are known which operate at frequencies in the microwave range in order thus to determine the distances between the code transmitter and the vehicle by using radar methods.
For the communication of the transmitting and receiving units with the base unit, electrical lines are laid within the motor vehicle. If it is additionally desired to carry out a distance measurement in connection with the antitheft protection system, the requirements made of the electrical connections between the transmitting and receiving units and the base unit are elevated, since signals with high data rates or with a very large bandwidth have to be transmitted to the central base unit. Such cabling is extremely costly both on account of the radio frequency cable required and on account of production.
In order to avoid the cabling outlay between the transmitting and receiving units and the base unit, it is possible to evaluate the signals directly at the vehicle antennas in the transmitting and receiving units. However, this necessitates the use of highly complex and therefore costly antenna modules. Complex and costly antenna modules are necessary, in particular, if the latter are intended to be able to determine the distance between vehicle and code transmitter and thus to provide the abovementioned advantages of a distance measurement.